It has been common knowledge for many years that traces of gold, silver, platinum and other valuable metals are found in natural waters such as sea water and fresh water lakes and streams, and that these traces are present together with considerably larger quantities of other non-precious metals such as silicon, iron, magnesium and copper. U.S. Pat. No. 2,086,384 to Lady discusses the chemical recovery of these metals which are found in natural waters. U.S. Pat. No. 3,819,363 to Wanzenberg suggests a process for the recovery of precious metals from the sediment in sea water, the precious metal taking the form of organometallic precious metal values which are contained in organic underwater deposits on the surface of inorganic materials such as sand, pebbles or shells, hereinafter referred to as debris, which is dredged and then treated according to the Wanzenberg process. The steps in that process include detaching the organic phase from the inorganic debris by treating with benzene, and then recovering the organic materials by floating them as a froth to separate them from the inorganic debris which sinks. The recovered organic froth is then chemically oxidized to spontaneously combust organic components leaving the metallic values, which are subsequently treated by metal-winning steps of a conventional nature.
The present disclosure differs from the Wanzenberg process because the present disclosure teaches steps which do not appear in the Wanzenberg process, and because the Wanzenberg process relies upon steps that would be inoperative in the presently disclosed process. In the present disclosure active bacteria is initially introduced to imbibe, concentrate, and immobilize, metal values to remove them from the waste waters wherein such metal values appear in very low concentrations, thereby capturing them in an organic phase.
Conversely, Wanzenberg is not concerned with those precious metal values which are carried in the waters, and therefore his process does not teach a method for immobilizing these precious metal values and extracting them from the waters themselves. Instead, Wanzenberg teaches a process for separation of a precious metal-bearing organic deposit from associated inorganic debris using benzene which serves the dual purpose of accomplishing detachment of the organic deposit or coating, and also of forming a buoyant froth in which the organic matter containing the metallic values is floated free from the debris and made easily recoverable from the water. Treatment of the Wanzenberg type with benzene applied to the mixed organic/inorganic sewage sludge which occurs at one stage in the steps of the present process was tried, but in the present process this Wanzenberg step was found to achieve no useful separation.
It is known that certain rather specialized bacteria can be used for the recovery of various metals including precious metals from mixtures containing them, U.S. Pat. No. 2,829,964 to Zimmerley appearing to be the first to suggest the use of such a biological process employing ferrooxidans for dissolving sulfide minerals and for changing ferrous sulfate to ferric sulfate. Certain other patents teach the use of ferrooxidans as oxidizing bacteria useful in the recovery of certain metals such as copper from solutions containing them, these patents including U.S. Pat. No. 3,252,756 to Goren; 3,266,889 to Duncan et al.; 3,305,353 to Duncan et al.; 3,347,661 to Mayling; 3,607,235 to Duncan et al.; and 3,679,397 to O'Connor et al.
Another strain of bacteria referred to as denitrificans is used in the recovery of other metals from salts as taught in U.S. Pat. Nos. 3,105,014 to Harrison and 3,272,621 to Zajic. Still another strain of bacteria known as thiooxidan is discussed in U.S. Pat. No. 3,433,629 to Imai et al. and in U.S. Pat. No. 3,455,679 to Mayling. In each of these patents the process is essentially one of leaching to obtain selected metals in the form of other compounds which can be further treated.
However, none of these patents suggests the use of bacterial imbibing to capture metal values followed by burning off of the organic phase, for instance by incineration per se, or incident to smelting, to concentrate the metal bearing components.
There are other patents using biological treatment steps which are of interest in connection with the present subject matter since they involve the use of an activated sludge in the recovery of metals. U.S. Pat. No. 3,218,252 to Glover et al. teaches the use of an activated sludge process for the bacteriological oxidation of ferrous salts in an acid solution in which the bacteria is a ferrooxidan. The object in the Glover process is not to recover the iron per se, but to remove from mine waters metal compounds which are considered to be pollutants. The separation of the oxidized metal is accomplished by precipitation, after which part of the activated sludge is returned to the input stage of the process for recirculation with new mine waters being introduced thereinto. Thus, the metallic component can be separated from the organic component by precipitation because it can be differentiated by physical properties, the organic matter passing off with the treated mine waters.
Still another technique involves the recovery of silver from a solution containing silver halide, where the silver is in a gelatin, by using the step of fermentation of the gelatin in contact with an aerobic bacteria. An example of this process is U.S. Pat. No. 3,501,378 to Shinkai.
U.S. Pat. No. 3,537,986 to Watanabe et al. is a patent teaching the use of activated sludge to reduce the amount of coagulant needed to recover silver halide from a solution including gelatin by oxidizing and decomposing the gelatin, whereupon the silver halide is adsorbed on the sludge which is then precipitated, leaving supernatent liquid also containing unprecipitated silver halide. This patent contains no suggestion that bacterial action in waste waters would capture and immobilize precious metal values appearing in the waters in such dilute concentrations as to be unrecoverable by the use of coagulents. It contains no teaching of incineration in order to concentrate the metallic component, and it fails to teach the inorganic metal-winning steps which are required to achieve recovery of the precious metal values in the presence of much greater concentrations of the metallic values appearing as contaminants.
U.S. Pat. No. 3,755,530 to Avila et al. is not a biological process, but seeks to recover metals from plating solutions by a freeze-drying method which involves sublimation of the frozen solution followed by roasting of the dried agglomerates, the roasting serving the purpose of decomposing metallic salts, rather than serving the purpose of concentrating such salts by removal of organic flocculents with which the metal-bearing values are mixed as is the case in the present process.
Canadian Pat. No. 983,722, filed Aug. 31, 1972, in the name of Matyas Korosi and issued to Eastman Kodak Company teaches the recovery of silver from the waste waters of emulsion manufacture containing gelatin by treating the waters with a certain enzyme which reacts with the gelatin to form soluble peptides; then acid treating to effect precipitation of silver metal or compounds; then separating a concentrate of silver metal. The specification mentions incineration as a part of the silver recovery process.
With regard to treatment of the metal bearing ash to recover the desired metals therefrom, there are a great many prior art teachings including various different approaches, comprising pyrometallurgical and hydrometallurgical techniques which are typical of the metal-winning steps in the present process. These steps are of course non-biological and generally involve inorganic chemical recovery of the metals.